This invention relates to padding structures in general and has specific reference to resilient padding structures for automotive use.
1. Field of the Invention:
In many fields, especially automobile construction, there is an increased trend towards a general use of elements having elastic, shock-absorbing properties. Thus such elements are widely used for lining the passenger compartments of many types of motor vehicles, especially the instrument panel or facia board.
In the following disclosure the problem lying at the root of this invention and the solution proposed therefor will be set forth, for the sake of simplicity and clarity, with specific reference to an instrument panel of motor vehicle, but of course this choice should not be construed as limiting the scope of the invention, since the latter is applicable to many composite elements whether or not intended for the automotive industry.
2. Description of the Prior Art:
One-piece instrument panels of cellular plastic such as polyurethane are already known; they are obtained by using a molding process performed under such conditions that a "skin" builds up automatically on the outer surface of the instrument panel to constitute the visible portion thereof. This process is not only very delicate to carry out, but requires the use of very expensive molds of relatively short useful life, these molds being usually made from silicone materials.
To reduce the cost of these instrument panels an obvious solution seemed to be to substitute, for this skin formed integrally by molding with the instrument panel body, a plastic sheet, for example of PVC, independent of, but adhering to, this panel body. To this end, it was only necessary to cast the resin or resin mixture into a mold having its two registering faces lined respectively with the plastic sheet and with a rigid supporting element to be subsequently used as a support for the composite assembly.
However, even in this case drawbacks were found, in that the outer sheet and the inner padding or stuffing had different coefficients of thermal expansion, so that the bond between these elements was not sufficient and the sheet tended to become detached from the padding.
To avoid this unsatisfactory bond a known proposition consisted in forming ribs on the inner face of the plastic sheet, preferably in the form of a checkered pattern. However, better results were not achieved because these ribs acted as barriers counteracting the expulsion of air during the resin -injection operation, so that eventually air pockets developed along these ribs and proved highly detrimental to the bond between the outer sheet and the inner cellular padding.
With this history, it hardy seems to be possible, up to now, to make a composite unit comprising a rigid support, a cellular padding and a plastic sheet, with a bond, between the cellular padding and the plastic sheet, sufficient to positively prevent the separation and tearing off of the plastic sheet.
This gap is actually filled up by the present. To overcome this problem, the present invention provides a composite unit or assembly comprising at least one rigid support, a cellular padding and a plastic sheet, this assembly being characterised in that the plastic sheet comprises on its back or inner face a large number of studs constituting as many anchoring means penetrating into the cellular padding and disposed with a relative spacing or pitch small enough to withstand tearing stresses caused by the differences in thermal expansion of the sheet and padding, and to distribute uniformly and proportionally, throughout the surface of the composite assembly, the dimensional variations due to the differences in shrinking and expansion of the component element of the assembly.
The aforesaid studs molded integrally with the plastic sheet, can have any desired configuration, provided that their resilience is sufficient to withstand the distortion resulting from the differences between the thermal expansions of the sheet and the cellular padding on which said sheet is caused to bear and react.
Of course, various materials may be used for making the three component elements of the composite unit of this invention. Thus, the resin support constituting the rigid or relatively rigid base of the assembly consist of metal or plastic material and the cellular padding advantageously consist of polyurethane. The plastic sheet and the studs formed integrally thereon may consist, preferably, of PVC.
The padding is prepared in situ in the mold, the two registering faces of this mold having been lined beforehand with the rigid support and with the plastic sheet respectively. This rigid support and this sheet are shaped beforehand in independent molds.
A clearer understanding of the present invention will be had from the following description with reference to the accompanying drawing.